To not let in-laws come round...

[ThrowItOnMe]

...once they've had their vaccinations? They live with 4 adults (their grown up children and partners) and a preschooler who goes to nursery.
I'm worried that if someone in their household gets the virus, the in-laws could still pass it to us even though they'll have had the vaccination.
In-laws keep trying to come over but I keep saying no. We've had covid but I would hate to pick virus up again and my children pass it to their teachers. They are in school twice a week. Part of me wants to say sod it, let the kids see their vaccinated grandparents but then I know the teachers are trusting us not to give them the virus. I'm talking in about 3 weeks time. I would feel differently if my in-laws lived alone and able to shelter from potential contacts.

Is there no lockdown where you live, OP? Socialising indoors with other households is an offence carrying a fine, surely? You could simply tell the ILs that you are not prepared to break the law.

YANBU. In-laws want to have their cake and eat it too. Lockdown rules apply to them too.

Given that the line is that vaccines only reduce the major symptoms, pretty certain they can still get it and pass it on.

Vaccination doesn't mean they cannot pass it on. They need to continue to observe lockdown, to protect others. Until the majority of people are vaccinated we are still going to have restrictions.

I need to form a childcare bubble so I can work. I've not been able to home school and work so my work has really suffered. I'm not furloughed.
Just don't know what to do anymore.
In-laws keep asking to come over and it would be massively helpful to have a childcare bubble, but you're right, we are still in lockdown and they could still potentially pass the virus to us and my kids take it to school (they go twice a week).

I will continue to stand strong and say that we can't mix households even though they've had the vaccine. You're right, they can definitely still carry the virus if when they've been vaccinated, they just won't be poorly from it (hopefully).

It just feels so unfair when I know so many people where their kids are spending time with their grandparents as a childcare bubble.

If you genuinely need them for childcare, I would. As long as everyine involved is happy with the risk which is a very personal decision.